1. Field of the Invention
The present invention relates to layout structure of a power steering system for a vehicle, and more particularly to layout structure of an actuator.
2. Description of Background Art
A conventional layout structure of a power steering system for a vehicle is known wherein the power steering system is arranged in a front part of a body frame by coupling the front end of an actuator for constituting the power steering system to a steering shaft and installing the rear end of the actuator to a component part of the body frame. See, for example, Japanese Patent Laid-Open No. 2617208, FIGS. 1 and 3.
FIG. 10 of the drawings corresponds to FIG. 3 of Japanese Patent Laid-Open No. 2617208. The reference numerals in FIG. 10 have been re-designated as compared to FIG. 3 of Japanese Patent Laid-Open No. 2617208.
FIG. 10 is a side view of principal part showing a conventional layout structure of a power steering system for a vehicle wherein the body frame is provided with: a main pipe 301 provided in the upper part; a front pipe 302 extending forward and obliquely downwardly from the front end portion of this main pipe 301 and an under pipe 303 which is curved downwardly from the lower end of this front pipe 302 and extends backwardly. A front cushion pipe 304 is laid between the front pipe 302 and under pipe 303 and a hold pipe 306 under the steering is laid between the front pipe 302 and front cushion pipe 304. The rear end of a power assisting actuator 311 is provided for constituting the power steering system and is installed to a pipe end 307 extending from the hold pipe 306 under the steering via a vertical shaft 308 and the front end of the power assisting actuator 311 is coupled to the steering shaft 312.
When the power assisting actuator 311 is operated and an assisting force is applied to the steering shaft 312, a reaction force is generated in the power assisting actuator 311 itself. Therefore, the pipe end 307 requires strength and stiffness for supporting the above-described reaction force. However, if the pipe end 307 is shaped like a cantilever beam, for example, the sectional shape must be taken into consideration. Thus, the sectional area is made larger and a reinforcement must be made in order to prevent its deflection from becoming great, resulting in an increase in cost.
Further, when the power assisting actuator 311 is shaped like a cylinder, the way the longitudinal direction having a long and narrow shape is arranged in the body frame will affect the degrees of freedom in design such as the shape and size of the auxiliary parts to be installed around it.
FIG. 11 of the drawings corresponds to FIG. 1 of Japanese Patent Laid-Open No. 2617208. The reference numerals for FIG. 11 have been re-designated as compared to FIG. 1 of Japanese Patent Laid-Open No. 2617208.
FIG. 11 is a side view showing a vehicle equipped with a conventional power steering system wherein the steering shaft 322 is installed on the body frame 321 of the vehicle. On the upper end of the steering shaft 322, handlebars 323 are installed and to the lower end thereof, the steering arm 324 is installed. A knuckle arm is coupled to the steering arm 324 via a tie rod with the front wheel 326 being supported by this knuckle arm. To the lower part of the steering shaft 322 a hydraulic power assisting actuator 327 is coupled for constituting one portion of the power steering system. In FIG. 11, an engine 331 is arranged in the rear of the power assisting actuator 327 and installed to the body frame 321. An exhaust pipe 332 extends from the front part of the engine 331 towards the rear of the vehicle body.
The power assisting actuator 327 is connected to hydraulic piping extending from, for example, an oil pump and a reservoir tank. Thus, when the hydraulic piping and the above-described exhaust pipe approach to each other, heat countermeasures such as providing the hydraulic piping with a heat insulator becomes necessary so as not to be affected by heat from the exhaust pipe. If such heat countermeasures are taken, the space around the power assisting actuator 327 will be narrowed and the degrees of freedom in design of the power steering system such as the power assisting actuator and the hydraulic piping, the exhaust piping and the engine will be reduced.